A process for producing graphite comprising heating at least one polymer film selected from polybenzothiazole, polybenzobisthiazole, polybenzoxazole and polybenzobisoxazole at 1,800° C. or more to convert the film into a graphite (Patent Document 1) has been known as a process for producing a graphite film having excellent thermal conductivity.
The graphite obtained by the process of Patent Document 1 has extremely high thermal conductivity, and is therefore used as a heat radiation member in electronics. The graphite is specifically used in 1) a heat radiation spacer held between a CPU and a cooling fan or heat sink or 2) a heat radiation spreader attached to a DVD optical pickup or enclosure to diffuse heat, for example.
A graphite must be actually attached to a heat generating component using an adhesive or pressure sensitive adhesive. Graphite is easily separated from the surface of the graphite obtained by the method of Patent Document 1 and the graphite obtained by the method is in a foaming state. Accordingly the graphite has an inferior adhesive force, and cannot be attached to a heat generating component or cannot exhibit sufficient heat radiation capability.
The graphite obtained by the method of Patent Document 1 has a low surface hardness. When the graphite is attached to electronics or handled, the surface of the graphite is damaged and graphite is separated from the damaged area. Thus, the inside of the electronics is contaminated, or the graphite cannot exhibit sufficient heat radiation capability.
In particular, as the thickness of the raw material film is larger, graphite is easily separated from the surface of the graphite and the graphite is in a foaming state. Accordingly, hardness of the film is reduced. Further, the film has a decreased thermal diffusivity, has a lower strength and is easily broken. On the other hand, a graphite film must be thick in order to have improved heat radiation properties. Improvement of thermal conductivity cannot be achieved at the same time with use of a thick polymer film as a raw material.
Patent Document 1: Japanese Patent Laid-open No. 61-275115